The majority of oils and certain fats used in food, cosmetic and pharmaceutical products are rich in polyunsaturated fatty acids and, because of this, are particularly sensitive to oxidation. Their stability can be improved by the addition of synthetic antioxidants such as, for example, BHA (butyl hydroxyanisole), BHT (butyl hydroxytoluene) or TBHQ (tert.butyl hydroquinone). Unfortunately, the harmlessness of these compounds is questionable.
Attempts have been made to replace these synthetic antioxidants with natural antioxidant compounds of the fat-soluble type such as, for example, the tocopherols or ascorbyl palmitate or of the water-soluble type such as, for example, ascorbic acid, vegetable extracts, organic acids or amino acids. In the case of the water-soluble compounds, an emulsifier, such as a phospholipid for example, has to be used for incorporating the water-soluble antioxidants in the oils in the form of micelles.
By virtue of their structure, the phospholipids are capable of creating associations with certain water-soluble compounds to form micelles which, for their part, are fat-soluble.
The incorporation of vitamin C or other water-soluble compounds in oils using phospholipids is known, for example, from European patent application 0 326 829. Unfortunately, this known process uses an organic solvent, for example ethanol, which promotes the formation of a single phase in view of its hydrophilic and lipophilic properties. In addition, the process in question--which uses an unfractionated soya lecithin--is attended by the disadvantage that problems of color, odor and flocculation in storage cannot be avoided.
According to U.S. Pat. No. 5,084,289, inverse micelles, i.e. micelles in which the continuous phase is the lipophilic phase, are formed by dissolving in an oil a phospholipid and then a small quantity of an aqueous solution containing a water-soluble antioxidant, for example vitamin C, in a high concentration. The mixture is stirred to form inverse micelles, a single phase thus being obtained. The small quantity of aqueous phase relative to the lipidic phase makes homogenization difficult or even virtually impossible on a large scale. In addition, it is only possible by this process to incorporate substances highly soluble in water, for example vitamin C, and not sparingly water-soluble substances such as, for example, ethylene dinitrotetraacetic acid (EDTA). Finally, this process does not avoid the appearance of undesirable colors and odors in storage because the lecithin is not fractionated.
It has now surprisingly been found that these disadvantages can be completely eliminated by using a phospholipid fraction substantially free from phosphatidyl choline.